1. Field of the Invention
The present invention relates to electrical devices using nanostructures, for example, nanotubes or nanowires, as a conductive element.
2. Description of Related Art
Electronic devices using nanostructures as electrical conductors are useful as transistors, optoelectronic devices, and chemical and biological sensors. Nanostructures that have been used in such devices include carbon nanotubes and silicon nanowires. For a variety of reasons, it is desirable to modify the nanostructures. Modified nanostructures can have improved electrical characteristics, greater sensitivity to chemicals, or greater specificity in their sensitivity to chemicals. However, these modifications can be difficult to effect. Some modifications have been made to nanostructures in solution, before they have been incorporated into a device. This approach is limited to those nanostructures which can be readily put into solution.
Nanostructures on substrates have been modified by the addition of metal. Specifically, physical vapor deposition has been used to produce thin films of metal on the substrates on which the nanostructures are disposed. As a result, the nanostructures are also coated with solid metal. By careful choice of the deposition conditions, the metal can be induced to form into nanoparticles. These particles coat the substrate and the nanostructures uniformly, which may be undesirable for some applications. Lithography can be used to restrict the formation of the particles to defined regions. But the minimum size of these regions is limited by the techniques of lithography, and within these regions the particle coatings are uniform.
A exemplary problem arises by the incorporation of nanotubes into electronic devices for use as hydrogen sensors. Nanotube electronic devices which operate as transistors can be coated with palladium to enhance their sensitivity to hydrogen. However, the uniformity of the coating within lithographically-definable regions of minimum size prevents the electronic devices from operating as transistor-type sensors. The nanoparticle coating is too conductive relative to the semiconducting nanostructure. If the palladium coating could be deposited on the nanoscale architecture of the sensor device in a more controlled fashion, the characteristic transistor properties could be preserved. It should be apparent that this problem is not limited to the deposition of palladium onto nanotubes devices, and may be encountered in any nanoscale electronic device for which it is desired to selectively deposit nanoparticles of a material on or adjacent to a nanostructure, such as a semiconducting nanostructure.
It is desirable, therefore, to better control the deposition of nanoparticles, such as metallic nanoparticles, onto selected regions of a nanoelectronic device. For example, it is desirable to deposit nanoparticles of different types on different regions of a nanoelectronic device. In addition, it would be desirable to provide nanoelectronic devices that take advantage of greater control over nanoparticle deposition.